The invention is in the field of fluid control. More particularly, the invention is a multi-piston spool valve capable of controlling the flow of fluid to a dynamic hydraulic component, such as a hydraulic actuator or motor. The valve enables either zero, restricted or full fluid flow to the hydraulic component, thereby allowing multiple stages or levels of control of the component. A user of the invention is thereby provided with the ability to cause the controlled component to make rapid, major movements, or slower, more precise movements.
The valve""s functionality is achieved using a system of multiple pilot valves that act on associated pistons located within the valve. The valve""s spool is moved through the action of at least one pilot piston. One or more stop pistons are employed to limit the movement of the pilot piston(s).
The flow of fluid to a hydraulic actuator, hydraulic motor, or other dynamic hydraulic device is often controlled through the use of a pilot-operated spool valve. In most cases, the spool valve is used-solely to provide directional control whereby the controlled device either receives no flow, maximum flow in a first direction, or maximum flow in a reverse direction. To accomplish this functionality, the pilot acts to cause a maximum movement of the valve""s spool. Once the spool has moved fully in one direction, maximum fluid flow is enabled to the controlled hydraulic device. To cause the controlled hydraulic device to stop or reverse direction, a reverse movement of the valve""s spool is required. It should be noted that when maximum flow is enabled, the controlled device moves at its maximum speed.
There are some applications where a pilot-operated spool valve is employed to provide proportional control of a hydraulic component. In this type of application, it is usually desired to cause the controlled hydraulic component to move at speeds greater than zero but less than the component""s maximum speed. In some applications, proportional control is achieved using a spool-type servovalve.
One example of a servovalve designed to give a user proportional control of a dynamic hydraulic device is taught by Sloate in U.S. Pat. No. 4,674,539. The Sloate servovalve makes use of an electric motor in combination with threadedly-engaged members to slowly cause the translation of the servovalve""s spool. However, the speed of operation of such a unit is severely limited. Sloate notes that changing the thread ratios employed in the device can change the speed of operation.
Proportional control of a hydraulic component enables precision control of the component. However, there are times when it would be desirable to have multi-speed control of a hydraulic device. This type of control would offer both simple directional control and precision proportional control of the hydraulic component.
A first example where multi-speed control is desirable is found when a hydraulic motor is connected to a winch. It is often advantageous to initially lift a load at a low-speed, giving one a chance to assess the security of the lifting harness, before lifting the load at full speed.
A second example may be found when a hydraulic motor is used to operate a cooling fan. A typical arrangement would employ a control valve that enables the fan to run at full speed, or not at all. There may be certain conditions or situations where one or more intermediate speeds are desirable.
A third example is presented in some marine steering systems, where a hydraulic actuator is connected to a rudder or water deflector. In this type of application, it is desirable during relatively high-speed operation of the vessel for the rudder or water deflector to move fairly slowly. This enables a precise steering control of the vessel. When traveling at a relatively low speed, such as during docking maneuvers, one needs to move the rudder or water deflector at a very high rate in order to obtain the necessary movements of the vessel in an appropriate amount of time. In addition, when the vessel is docked, it may be beneficial to rapidly move the rudder/water deflector to a predetermined storage position.
There are many other situations where multi-speed control of a hydraulic component would be advantageous. The situations would usually also require the control system to be relatively low in cost, extremely durable and highly reliable.
The invention is a multi-piston spool valve capable of controlling a dynamic hydraulic component, such as a hydraulic actuator or motor. The valve allows a user to enable either a zero, restricted or full fluid flow to the hydraulic component. When a restricted flow of fluid is enabled, the user can achieve slow, precise movements of the component. When full fluid flow is enabled, the user can cause major, maximum-speed movements of the controlled component.
The operation of the valve is accomplished using a system of pilot valves. The system comprises a primary pilot valve arrangement (primary pilot) and at least one secondary pilot valve (secondary pilot). The primary pilot is operatively connected to at least one pilot piston located in the spool valve. The spool is operatively connected to the pilot piston(s) whereby the pilot piston(s) function to cause a translation of said spool. The secondary pilot is operatively connected to at least one stop piston located in the spool valve. The stop piston(s) function to oppose/limit the full movement of the pilot piston(s).
When full fluid flow to the component is desired, the primary pilot directs pressurized fluid into a chamber in the spool valve that is located adjacent a pilot piston. The fluid then applies pressure on one end of said pilot piston. This causes the pilot piston, and the operatively-connected spool, to move. Without any opposition from the stop piston(s), the pilot piston and spool can move to their maximum extent. This results in an outlet port in the spool valve being fully uncovered, thereby enabling the maximum rate of fluid flow to the controlled hydraulic component.
When a restricted flow of fluid to the component is desired, the primary pilot and at least one secondary pilot are actuated. When only one secondary pilot is employed, the secondary pilot sends pressurized fluid into a chamber associated with a stop piston. This causes the stop piston to be positioned at a predetermined location. At the same time, the primary pilot acts in the same manner as previously described, sending pressurized fluid into a chamber in the spool valve and causing a pilot piston to move the spool. However, the movement of the pilot piston and the spool is stopped short by the stop piston. As a result, a fluid outlet in the spool valve that leads to the controlled component will be only partially uncovered, resulting in a restriction in the fluid flow path. This leads to an intermediate flow of pressurized fluid to the controlled hydraulic component.
When the spool valve includes multiple stop pistons, multiple secondary pilot valves (secondary pilots) are employed to control the movement of the stop pistons. The multiple stop pistons interact to provide multiple limit stops that affect a pilot piston""s allowed travel. When two stop pistons are employed, the spool valve will be capable of providing five levels or stages of fluid flow to the controlled hydraulic component.
A fluid flow control valve and system in accordance with the invention is relatively low in cost and requires a minimal number of solenoids to control the valve""s operation. The system""s simple design enables it to be highly reliable and extremely durable.